The invention relates to positioning devices used to reproducibly fix the position of pallets along a conveyor, indexer or other transport device so that work can be performed on a product located on the pallet. As used herein, the term xe2x80x9cconveyorxe2x80x9d is used to refer to any of the various mechanisms used to transport products located on pallets for product assembly or similar purposes.
In order to keep pace with modern manufacturing methods, manufacturing line conveyors must move quickly and position the work accurately. Previously used positioning systems carried the work forward on pallets, and used feed pins to push or otherwise advance the pallets in the direction of conveyor travel (referred to as xe2x80x9cx-directionxe2x80x9d) and horizontally perpendicular to the direction of conveyor travel (referred to as xe2x80x9cy-directionxe2x80x9d). In some cases, the previously used systems used positioning pins, often termed xe2x80x9cshot pinsxe2x80x9d, to fix the position of the pallets in all three spatial directions (including the direction vertically perpendicular to the direction of conveyor travel, or xe2x80x9cz-directionxe2x80x9d) to achieve accurate positioning at particular points along the manufacturing line.
However, the previously used systems typically relied on feed pins and shot pins which were oriented obliquely or transversely to each other. The obliquely or transversely oriented pins are difficult to sequence precisely properly. They also give rise to complicated time-variant, three-dimensional loads which cause unnecessary vibration. Additionally, the previously used two- and three-directional pin positioning systems are complicated to construct and maintain. The trend in manufacturing is toward ever faster operating speeds.
A need exists for an improved system for fixing the position of pallets for conveyors, indexers and other manufacturing line transport systems. Preferably, the improved system is simpler and faster in operation, is easier to adjust and generates less onerous vibration than previously used systems. More preferably, the improved system needs only one fixing pin to accurately fix the position of a pallet bearing the work when the pallet arrives at a manufacturing station.
The invention provides a system which utilizes a single pin with a special head, called a xe2x80x9cshot pin,xe2x80x9d to fix the position of a grooved work pallet at each manufacturing station in a manufacturing line. The shot pin and a feed pin for advancing the pallet move simultaneously along parallel lines in the same direction to accomplish their individual functions. The shot pin fixes the position of the pallet at the work station in the x-direction, the y-direction and the z-direction. Because the feed pins and the shot pin move in tandem, they can operate relatively quickly without applying unnecessary torque to the conveyor or the pallet.
When the pallet arrives at a manufacturing station, the head of the shot pin moves toward the groove in the pallet until the head locks the pallet in the desired position. At the same time, the feed pin moves along a parallel line in the same direction to disengage the pallet. When work is completed at the manufacturing station, the head of the shot pin moves away from and releases the pallet. Simultaneously, the feed pin moves to engage and take control of the pallet. The feed pin then moves to advance the pallet along the manufacturing line.
A datum bar registers the pallet in relation to one or more registration surfaces, such as a top surface and a side surface. These registration surfaces cooperate with corresponding registration surfaces of the pallet, such as a bottom surface and a side surface, to guide the pallet as it travels along the manufacturing line under the influence of advancing feed pins.
Preferably, the feed pin and the shot pin move simultaneously along parallel lines in the same general direction. This desirable relationship between the feed pins and the shot pin is referred to as operating xe2x80x9cin tandemxe2x80x9d or xe2x80x9cin-phase.xe2x80x9d Tandem movement permits the shot pin to fix the pallet at the same time that the feed pin releases the pallet. Tandem movement also permits the shot pin to release the pallet at the same time that the feed pin engages the pallet. Adjusting the sequence and timing of tandem movement is relatively easy. Also, the vibration generated by tandem movement is typically less complicated and easier to dampen or otherwise deal with than the vibrations generated by obliquely or transversely oriented pins.
The shot pin is one component of a shot pin assembly, which additionally includes a bushing, a spring and a retaining washer. The shot pin has a shaft that is of circular cross section or, alternatively, of elliptical or polygonal cross section. The head of the shot pin is preferably shaped as the frustum of a truncated cone or the frustum of a truncated pyramid, more preferably as the frustum of a truncated sphere including, but not limited to a hemispheroid. The shaft passes through the bushing and the head mates with the groove to register and correctly position the pallet when the head is urged into the groove. The groove communicates with a depression or hollow in the pallet and is shaped to receive the shaft and head so as to accomplish this purpose.
When assembled, the bushing is preferably located in a hole in the datum bar. The internal and external clearances of the bushing in each direction are controlled to provide the degree of accuracy and precision in locating the pallet along with conveyor as required by the manufacturing station.
Because the shot pin positions and fixes the pallet simultaneously in the x-direction, the y-direction and the z-direction, the fixing process is simple and fast. A single motion quickly fixes or releases the shot pin relative to the pallet. By fixing the position of the pallet quickly and employing feed pins which operate in tandem with the shot pin, it is possible to begin work sooner on the product carried by the pallet and accomplish more work within a given time period.